Chad,

I looked in to doing the same thing but couldn't find much other than it appears to be incredibly difficult, if not impossible.

An alternative to the out-of-the-box SSRS front-end:

http://crisscross.codeplex.com/

The developer was in a similar position and couldn't make the necessary edits and decided to create his own front-end for his reports.

Check it out and see if it helps.

Mark